The Processing Unit
You can obtain cluster information about the topology, member ID and other related parameters. Cluster information can be provided to the processing unit instances at deployment time. You can also reload business logic (Spring beans) without shutting down the application or undeploying a Processing Unit.
If you want to build a Custom Processing Unit, you can can implement the ServiceDetailsProvider and ServiceMonitorsProvider interfaces to expose information to calling APIs, or to be viewable in the Web Managment Console.
In order to deploy and run the Processing Unit, you have to choose the appropriate runtime mode and possibly do some debugging. There are also a number of deployment properties that can be set.